Automatic slack adjuster for railway brakes and the like



June 29 1926.

' A. R. K. DJURSON UTOMATIC SLACK `A-DJUSTER FOR RAILWAY BRAKES AND THE LIKE Filed Feb. 5, 1926 lull.

dans 25, 1925.

UNITED STATES PATENT FFICE.Y

AXEL RUDOLF KONRAD DJURSON, F MALMO, SWEDEN, ASSIGNOR T0 SVENSKA AK- TIEBOLAGET BROMSREGULATOR, OF MALIVIO, SWEDEN, A CORPORATION OF SWEDEN.

YAUTOMA'IIC SLAGK ADJUSI'ER FOB, RAILWAY BRAKES ANDvTHE LI KE.

Application filed February 5, 1926, Serial No. 86,344, and in Sweden March `14, 1925.

This invention relatesl to an automatic slack adjuster for brakes, and particularly for brakes for railway carriages and the like.

The object of the invention is to provide an improved device of this character having certain novelfeatures of constructionand operation hereinafter set forth.

In slack adjusters for railway brakes and the like of the type hitherto in use including such slack adjusters which are adapted to enlarge as well as to reduce the slack. between the brake shoes and the wheels, difliculties have arisen for the reason that, upon the unloading of a loaded carriage, the slack has been suddenly reduced with the conse-I quence that not only the length of stroke of the piston in the brake cylinder has been kept -under its normal value but also in some cases the carriage wheels have been entirely locked, so that a comparatively great number of braking operations will be necessary to restore the slack to its normal value.

The object of this invention is to elimi-` nate this drawback and to render possiblel the restoration of the proper slack by means of single braking operation. The inven-.

tion particularly relates to slack adju'sters in which a screw and nut device, that isan adjuster screw with cooperating nut means is used for increasing and decreasing respectively the slack, the rotary movement of thev screw and nut devicebeing dependent on a compulsorily controlled blocking device.

The characteristic feature of the invention substantially consists in that the angle of inclination ofthe threads of the screw and nut device is chosen so great as to avoid a self-locking of the device, so that the latter may be operated simply by the action of the tension which arises inthe brake rigging when the brake is applied, provided the compulsorily controlled blocking device is so set as to permit such operation.

The invention is illustrated in the accompanying drawing, in which Figure v1 on a reduced scale shows a diagrammatic elevation of the general arrangement of a brake cylinder and associated parts including a portion of the improved slack adjuster. Figure 2 shows in alarger scale a longitudinal section through the improved slack adjuster. Figure 3 is a side elevation of the one end of the slack adjuster including a member for the transfer of movement, some parts being shown in section. Figure 4 is a transverse section on the line adb, Fig. 2 looking in the direction of the arrows, an element being shown .outside of Figure 4 in a side elevation.

Referring to Fig. 1 the brake cylinder,

adapted for instance for compressed air, is

denominated as l and the rod of its pistonr ends of the brakelevers 3 and 4 approach each other. The slack adjusting vdevice may be mounted 1n one of the brake bars near its joint with the brake lever. The positionV of theslack adjusting device in intimated as 16, 18. l Y

The movement necessary for the operationl of the slackadjuster may be obtained through the intermediary of a bellrrankV lever`6, 7 p ivotally mounted on a stud 8 Fig.v V1 is fixed to a part of the slack adjuster see al soFig. 3). The one branch 6 of the bell crank lever is jointed to an iadjuster rod 9 which isjointed at itsvother end to the lowerA endof the brake lever 4, a resilient device Y 10 being inserted in the rod 9 and forming a resilient portion thereof.V When upon the application' of the brake pressure,'the lowerv ends of the brake levers approach each other a certain pressure is applied to the rod 9 which is transferred in the form of a longitudinal movement to the branch 6 of the bell crank lever which in its turn will swing about its pivot 8. The end of the other branch 7 of the bell crank leveris jointed to a member If the re.

movement through the intermediary of the bell crank lever 6, 7 ceases, and the excessive pressure applied to the rod will be absorbed by the resilient member' 10 which may consist of a helically wound compression spring.

It, however, is to be understood that the general arrangement of the slack adjusting device above described is to be considered a preferred Aform of embodiment and be varied within very `wide limits in accordance with the. construction of the brake system employed, the 'main fact of importance for the invention being that movement is transferred to the slack adjuster preferably through the intermediary of a resilient member which causes the movement to cease, when the resistance opposed to such movement Yreaches a predetermined maximum value. Thus, the movement may be also transferred inthe form ofa pull insteadof a pressure, and vfurther the .resilient member may consist of a tension spring instead of a compression spring.

In theslack adjuster (Figs. 2 and 4) the actual adjusting device consists as usually of Van adjuster screw 12 and .nut means 13 cooperating therewith but as Va differentiation from constructions hitherto known the screw `4and nut means are provided with threads the pitch of which is so great that the screw and nut members are not selflocking, that is to say that the knut member, for instance, is subjected to Ya rotary movement when a sufficiently great pressure or pull is applied .to the. screw member. The screw and nut device is preferably provided with multiplex threads. The screw 1E?. is securely fixed to a coupling socket '14e for one vof the brake bars (not shown) and the nut member 13 is freely .rotatably but axially not I'd'isplaceably connected to another coupling socket 15 which is jointed to the lower end ofthe brake lever 3 (Fig. 1). V`it therefore is obvious that a rotary motion of the -nut member 13 relatively to the adjuster screw 12causes a lengthening or shortening of the distance between the ypoints of fixation of the coupling-sockets Maud '15, which results in a corresponding increase or decrease of the lslack between the brake shoes andthe carri-age wheels. From it will be observed that `it is immaterial whether the screw or the nut receives a rotary movement, while -the other member remains `stationary, as a rotary motion of the one member in relation -to the vother member is the essential factor The lportion of the brake bar in which theslack adjuster is'iitted be'carried out in the form of a tube 16, as shown 'in Fig. .2, said tube carrying the nut member13. The tube 16 forms a protective casing for-the vportion of the screw 12which is projecting from theone side of the nut 13 and another protective casing 1T .is arranged about the other projecting portion of the screw 12-and fixed to the coupling socket 14,

the tube 16 telescoping in the casing 1f rThe blocking device which determines the adjusting effect of the slack adj uster is mounted within a housing 18 which preferably is integral with the coupling socket 15. Through the one end of the housing 18 extends a spindle 19, which is securely fixed to the. tube 16 and thus connected with thenut member 13. To the spindle 19 is attached within the housing 18 a flange like member 20, the axial surfaces of whichare alternatively incontact with correspondent friction surfaces 21 and 22 'provided "for lthis purpose within the housing 1S. In the `position of the parts shown in Figure 2 the 'flange like member Q0 is assumed to be in fric-`- tional contact with the friction surface 22. The flange 2O is kept in this position, when the brakes are in"oift position, by means ot a powerful compression spring QB mounted within the housing 18 and operating on thc flange like member Q0 through 'the intermediary of an anti friction bearing 24 for the purpose of reducing the 'f'riction produced by the rotation of the spindle. 19. About portion'of the spindle v19 preferably havingl a smaller diameter coupling mcmber' is journalled which has a flange '2G provided with ally extendingV ratchet teeth which are adapted-to cooperate with correspondingr axially extending from `the ratchet vteeth 2! flange like member 20, this latter serving as` the other coupling member of' the blocking device. A compression spring 28 of smaller dimensions than the spring and arranged between the ange Q6 and a flange like extension within the housing 18 permanently tends to bring the coupling members 26 and 27 in engagement with each other. The member 11 referred to above and cooperating with the bell crank lever 6, 7 (Figs. '1 andY 3) is a `forked crank which at least periferally is securely fixed to the coupling` member 25, and thus it is this coupling member to which the movement of the rod 9 is transferred through Vthe intermediary of the resilient member 10, the bell crank lever 6, 7 and the crank 11. For compulsoril-y controlling the blocking device formed by the two coupling members 26 and 27, v20 lthe housing 1S is provided on its interior walls with a number, preferably two, Xed projections adapted to cooperate with corresponding projections 30 radially extending from the flange 26 of the coupling member 25. These projections 29 and V30 are jprovided with inclined surfaces alt the sides facing each other, preferably in both directions, so that they comparatively easily may glide one upon the other, the interengagement oi the ratchet teeth of the two coupling members being released by surpressing the power ot Vthe spring 28 (the position as shown in Fig. 2) while the interengagement of said ratchet teeth is automacallyeifected by Vmeans of said spring 28, when the above ics described projections 29 and 30 are` out of registering position with each other (the po-v sition shown in Fig. t).

lVhen the brake is applied,`two`forces are produced, which are of importance for the proper function of the device. These forces are :-firstly, a force which hereafter may be called the controlling force and which is produced in the rod 9. This force actsthrough the intermediary of the bell crank lever 6, 7 and the crank 11 in the form of a rotary motion upon the coupling member 26, and secondly, a force in the tube 16 (that is part of one of the brake bars), which force is a function of the braking pressure and usually is in the form of a tension (but may also be a compression). This force may be called braking force. As the controlling force effects a rotary motion on the coupling member 26 and when this latter is in engagement with the other coupling member 27, 20 the nut member 13 consequently receives a rotary motion, provided the braking force has not reached a value which is greater than the value of the controlling force, but should this be the case the surplus movement in the brake rigging will be absorbed in the form of a reserve force in the resilient member 10.

The operation of the device is as follows Assuming normal slack between the brake shoes and the wheels and with the brake in off position, the projections 29 and 30 rest upon each other and prevent an interengagef ment of the coupling members 26 and 27, 20.

-Upon applying the brake until Ythe brake shoes just are in Contact with the wheels, the crank 11 is to be turned yto a certain predetermined position, in which the projections 29 and 30 have been angularly displaced so that the coupling members 26 and 27, 2O are in engagement with each other. Upon the continuation of the application of the brake pressure, a tension arises in the brake rigging and in consequence thereof the spring 23 is compressed and the flange like member 2O is axially displaced so that it abuts against the friction surface 21. The friction produced between the members 20 and 21 prevents a further rotary motion of the nut member 13 in relation to the screw 12 and the excessive movement of the rod 9 is absorbed in the resilient member 10.

Assuming by way of example, that the slack is too great. Upon the application of the brake pressure and when the crank 11 has reached the above stated predetermined position the braking force will not have reached such value that the spring 23 has been compressed and the flange like member 20 has come into contact with the friction surface 21, so that the nut member 13 will receive a rotary motion by the crank 11, which reduces the slack.

If, on the other hand, the slack has been too little', that is theV brake shoes are already in contact with the wheel before the crank 11 has reached its predetermined position, a tension is produced at an earlier stage in the brake rigging and the screw 12, which tension compresses the spring 23 to such a degree that the flange like member 2O is no longer in Contact with the friction surface 22, and as in this position of the crank 1l the coupling members 26 and 27, 20 are not in engagement with each other and as the threads of the screw and nut device 12, 13 have a non-locking pitch, any consequent pulling action on the slackv adjuster results in a rotary motion of the nut member 13 in relation to the screw 12 and thus in a corresponding lengthening of the slack adjuster, that is t-he slack will be enlarged.

Thus in both cases the adjustmentA becomes a function of the tension in the brake rigging, respectively a function of the time in which said tension reaches a normal value corresponding to the power of the spring 23, and in consequence thereof obviously one braking operation only is necessary for bringing the slack to correspond to the normal value of said tension, that is for bringin the slack to reach its normal value.

7Vhat I claim and desire to secure by Letters Patent is 1. In a slack adjuster for brakes, an adjuster screw and nut means, the angle of inclination of the threads of the adjuster screw and the nut means being so great as to prevent a self-locking of the adjuster screw in the nut means or vice versa, a compulsorily controlled blocking device which is rendered operative during a portion only of the braking operation, the one member of said blocking device being connected to said screw means.

2. In a slack adjuster for brakes, an adjuster screw and nut means, the threads of the adjuster screw and nut means being nonself-locking, a compulsorily controlled blocking device consisting of two members axially displaceable in relation to each other, the one member connected to the nut means, the other member connected with the brake rigging and receiving rotary motion from the latter upon the application of the brake.

3. In a slack adjuster for brakes, a nonself-locking adjuster screw and nut means, two blocking members facing each other and axially displaceable in relation to each other, the one member connected to the nut means, the other member connected with the brake rigging and receiving rotary motion upon the application of the brake, means tending to couple the blocking members together and means for pressing the blocking members apart.

1. In a slack adjuster forbrakes, a nonself-locking adjuster screw and nut means, two blocking members axially displaceable in rela-tion to eachother, 'an operative C011 nection ybetween the one 'member and the brake rigging for rotating the said member upon the -applicetionof the brake, the other member connected to the nut means and adapted to be displaced in the one direction by the action of the tension in the brake rigging and `in the other direction by the actionof-a resilient means, astop means for preventingsaid otherblocking member from rotating when the force of the resilient means is overcome :by .said tension in :the brake rigging.

In testimony whereof I have signed my naine to .this specification. 2

AXEL RUDOLF KNRD DJURSGN. 

